1. Field of the Invention
The corn earworm (CEW), Helicoverpa zea (also known as Heliothis zea), is a prominant pest of cotton, sorghum, tobacco and numerous vegetable crops, particularly corn, throughout the world.
This invention relates to a novel entomopathogenic nematode of the genus Steinernema, which is effective as a biopesticide for the control of insects, and particularly the corn earworm.
2. Description of the Prior Art
Recent studies have shown that the Lower Rio Grande Valley corn crop is a major source for the production of large populations of the corn earworm and fall armyworm which migrate north to infest corn and other crops of higher cash value such as cotton, tomatoes and soybeans, where they cause severe economic damage [Raulston et al., Production of Heliothis zea on Corn in Northeastern Mexico and the Lower Rio Grande Valley of Texas: a Potential Source for Corn and Cotton Infestation on the High Plains of Texas, Proc. Beltwide Cotton Conf., 1986, pp. 222-225Memphis, National Cotton Council of America; Wolf et al, Phil. Trans. R. Soc. Lond. B 328:619-630, (1990); and Pair et al, Florida Entomologist, 74:200-213, (1991)]. The primary control strategy for the corn earworm is the application of insecticides that result in egg and larval mortality. In Florida and other southeastern states, insecticides are usually applied at least every 48 hours to protect sweet corn during the silking period. However, the corn earworm has given indications of resistance to organochlorine and organophosphate insecticides [Wolfenbarger et al., Bull. Entomol. Soc. Amer., 27:181-185, (1981); and Sparks, Bull. Entomol. Soc. Amer., 27:186-192, (1981)]. This resistance, in addition to the wide public awareness of the environmental damage resulting from chemical pesticides, has increased interest in biological control, and has resulted in the study of a variety of biological control agents. Entomopathogenic nematodes have shown promise as biological control candidates for a number of insect pests.
Nematodes of the genera Steinernema and Heterorhabditis possess most of the characteristics of an ideal biological control agent for insects [Poiner, Taxonomy and Biology of Steinernematidae and Heterorhabditidae, In Gaugler and Kaya (eds.), Entomopathogenic Nematodes in Biological Control, CRC Press, Boca Raton, Fla., (1990), pages 23-61; and Gaugler, J. Nematol., 13:241-249, (1981)]]. These nematodes search for their insect hosts; they are highly virulent, killing most hosts within 48 hours; they are easily and inexpensively mass produced; and they have a wide range of insect hosts (Poiner, ibid and Gaugler, ibid). The effectiveness of these nematodes is attributed to a mutualistic bacterium of the genus Xenorhabdus associated therewith [Poinar, ibid]. After entry or penetration of the nematode into the insect host, the bacteria are released from the nematode and rapidly multiply, killing the host insect by septicemia. Conversely, the nematodes protect the bacteria from the environment prior to release within a suitable host. The pathogenicity of entompathogenic nematodes to Heliothesis species has been demonstrated previously [Tanada and Reiner, J. Inverteb. Path. 4:139-154, (1962); Bong and Sikorowski, J. Econ. Ent., 76:590-593 (1983); and Howell, J. Inverteb. Path., 33:155-158, (1979)]. However, there exists a negative relationship between larval age and susceptibility to the nematodes [Glazer and Navon, J. Econ. Entomol., 83:1795-1800, (1990); and Samsook and Sikora, Med. Fac. Landbouww. Gent., 46:685-693, (1981)]. Consequently, the use of these nematodes has been against the feeding stages of various insect pests, while their use against prepupal or pupal stages of H. zea has been limited.